The present invention is directed to a method for measuring electrical activity in the heart and a catheter useful for performing the method.
Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
In healthy humans the heartbeat is controlled by the sinoatrial node (xe2x80x9cS-A nodexe2x80x9d) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (xe2x80x9cA-V nodexe2x80x9d) which in turn transmits the electrical signal potentials throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of or damage to the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as cardiac arrhythmia.
Electrophysiological ablation is a procedure often successful in terminating cardiac arrhythmia. This procedure involves applying sufficient energy to the interfering tissue to ablate that tissue thus removing the irregular signal pathway. However, before the ablation procedure can be carried out, the interfering tissue must first be located.
One location technique involves an electrophysiological mapping procedure whereby the electrical signals emanating from the conductive endocardial tissues are systematically monitored and a map is created of those signals. By analyzing that map, the interfering electrical pathway can be identified. A conventional method for mapping the electrical signals from conductive heart tissue is to percutaneously introduce an electrophysiology catheter (electrode catheter) having mapping electrodes mounted on its distal extremity. The catheter is maneuvered to place these electrodes in contact with or in close proximity to the endocardium. By monitoring the electrical signals at the endocardium, aberrant conductive tissue sites responsible for the arrhythmia can be pinpointed.
Once the origination point for the arrhythmia has been located in the tissue, the physician may use an ablation procedure to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities and restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels.
Conventional unipolar electrode catheters utilize a primary tip or ring electrode that cooperates with a reference electrode outside the patient""s body. Such catheters are known to map inaccurate electrical readings due to the reference electrode being located outside the patient""s body.
Previous attempts have been made to design a bipolar electrode catheter having two electrodes within the patient""s body. However, such catheters also have limited accuracy. Specifically, both electrodes pick up near field electrical signals emanating from the conductive endocardial tissues due to their contact with the heart tissue, and far-field electrical signals which propagate from other regions of the heart due to their contact with the blood. The far-field signals interfere with the near-field signals, making accurate measurement of the near-field signals difficult. Accordingly, a need exists for a bipolar electrode catheter that more accurately measures near-field signals.
U.S. Pat. No. 5,749,914 to Janssen discloses a catheter for removing obstructions from a tubular passageway in a patient. In one embodiment, Janssen describes a catheter having a distal end with a recessed annular ridge that defines a groove in which a plurality of electrodes are seated. The electrodes are sized so that they are recessed within the annular ridge. A return electrode is located on the catheter proximal to the recessed electrodes. The electrodes are connected to a radio-frequency energy source that generates and supplies current to the electrodes to ablate constructive material. Janssen nowhere teaches or suggests, however, using this catheter to map electrical activity in the heart.
U.S. Pat. No. 4,966,597 to Cosman discloses a cardiac ablation electrode catheter with a thermosensing detector at a position in the distal end of the catheter. In one embodiment, the ablation electrode has an insulative exterior with openings that provide exposed electrode surfaces. Each of the electrode surfaces can be independently connected to different contacts, which are then connected to a voltage source, or the electrode surfaces can all be connected together. A temperature-measuring conductor is attached to one or more of the electrode surfaces. The object of the invention described in Cosman is to provide a cardiac catheter for tissue ablation with ultra-fast faithful recording of temperature in the affected tissue. Cosman nowhere discloses, however, obtaining electrical signals with different electrodes and comparing the signals to obtain near-field electrical activity information.
The present invention is directed to a catheter having two electrodes for bipolar mapping and a method for using the catheter. In one embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart. The method comprises introducing into the heart a catheter comprising an elongated tubular body having a distal region and a circumferential recess along the length of the distal region. A first electrode is mounted on the distal region in close proximity to the circumferential recess. A second electrode is mounted within the circumferential recess. The method further comprises positioning the distal region at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart.
In another embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart comprising introducing into the heart a catheter comprising an elongated body having an outer diameter and a distal region, a first electrode mounted on the distal region, and a second electrode mounted on the distal region in close proximity to and electrically isolated from the first electrode, the second electrode having an outer diameter less than the outer diameter of the portion of the distal region on which it is mounted. The distal region is positioned at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart.
In still another embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart comprising introducing into the heart a catheter comprising an elongated body having a distal region, a first electrode mounted on the distal region, and a second electrode mounted on the distal region in close proximity to and electrically isolated from the first electrode. The second electrode is covered by a blood-permeable membrane that prohibits direct contact between the second electrode and surrounding heart tissue. The distal region is positioned at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart.
In yet another embodiment, the invention is directed to a catheter comprising an elongated body having a distal region. A first electrode is mounted on the distal region. A second electrode is mounted on the distal region in close proximity to and electrically isolated from the first electrode. The second electrode is covered by a blood-permeable membrane that, in use, prohibits direct contact between the second electrode and surrounding heart tissue.